Share This Post:

Polygraph Tests: The Truth Won't Set You Free

In popular culture, there is a trope where the hero is called into a little
room, and a silent man hooks her up by electrodes to a machine. Paper
scrolls by wire arms which draw jagged lines as the hero is interrogated.
The results of this lie detector test will determine if the hero is caught,
or let go…

This trope exists because lie detectors, also known as polygraph machines,
do actually exist. They are actually used by many agencies, including
law enforcement, and scenes like the one described above actually occur.

But the secret of polygraphs is that as far as the courts are concerned,
they are unreliable, prejudicial, and inadmissible. So, even if you tell
the truth, the truth won’t set you free.

The fact of the matter is that in the hands of law enforcement agencies,
polygraph machines are essentially a prop. A polygraph examination is
a bait and switch.

The scene goes like this: a person is accused of a crime. Perhaps the police
have some evidence against the accused, but not enough to file a charge.
So, they try to get the accused to make an inculpatory statement. But
how will they get that person to agree to waive their right to remain
silent and to speak with an officer?

There are a variety of tactics to get someone connected to a polygraph,
but in my experience, many people are all too eager to for a chance to
“prove” that they didn’t do what they are accused of,
and readily agree to submit to a polygraph examination. They believe that
if they “pass” the test, the whole mess will go away.

But there is really no way to “pass” a test. There are no scientific
standards for a polygraph test, or qualifications of a polygraph examiner.
The little jags and squiggles produced by the machine reflect biometric
feedback from the person in the hot seat, but whether those jags and squiggles
spell out “lie” “or “truth” is a subjective
determination of the examiner.

A standard law enforcement tactic in any interrogation is to allow the
person to commit to a story, and then later confront them about what the
officer believes is a lie. A person might say, “How can I have punched
that guy? I wasn’t even at the party.” The interrogator, not
accepting that statement, might later confront the person on the claim:
“I know you were at the party. We have a witness that says they
saw you.” The officer may or may not actually have such a witness
(again, the police may lie to you) but by saying he does, he makes the
person being interrogated believe that the police have more evidence against
him than previously thought. If the person being interrogated was actually
at the party, but maybe not at the time of the assault, he may now admit
he was not telling the whole truth before, and the officer is one step
closer to closing his case.

A polygraph fulfills the same role as confrontation with a non-existent
witness. When a person says, “How can I have punched that guy? I
wasn’t even at the party.” The interrogator might say, “The
machine says you were being deceptive when you said you weren’t
at the party…”

People agree to take a polygraph because they believe if they tell the
truth, the machine will show it, and the truth will set them free. But
the officer knows that the while a polygraph will accurately show that
a person is nervous or sweating or tense during certain parts of an interrogation,
being nervous, sweating or tense is not proof of a lie any more than being
calm, collected and cool is proof of telling the truth. Even if the test
“shows” a person is being completely truthful when they deny
the accusation, the officer is under no obligation to discontinue the
investigation. If they believe the accusation is true and the denial is
false, they will forge ahead with their case, polygraph test or no.

The offer of a polygraph test by law enforcement is just a way to get a
person to make a statement that could be used against them. As always,
when you are
accused of a crime, what you need is a lawyer, not a law enforcement officer hooking you
up to a gizmo and asking you questions.